Half-Life 4: The Search For The Lost 3.

Try to throw the puzzle into sudoku.coach’s solver and you’ll find a ton of techniques that completely eliminate the guesswork.

I find sukdokus extremely fun and I never need to guess on a 6/7 out of 10 in difficulty. My suggestion is to take it slow at lower difficulties to get acquainted with the simpler techniques before springing to the harder difficulties.